Epidermal growth factor receptor (EGFR) inhibitors are commonly used in squamous cell carcinoma of the head and neck (SCCHN) but only a minority of patients derives benefit. SCCHN is the only cancer where EGFR inhibitors are part of routine management but mechanisms underlying sensitivity or resistance are not validated. The overall objectives in this proposal are to identify and characterize genomic alterations in SCCHN tumors that produce resistance to EGFR inhibitors as well as define mechanistic strategies to reverse resistance. The long-term goal of this proposal is to identify a subset of SCCHN patients that are highly likely to be resistant to EGFR inhibitors. Preliminary data support the hypothesis that activation of the phosphatidylinositol 3-kinase (PI3K)/AKT pathway, independent of the EGFR pathway, is a major mechanism of primary resistance to EGFR inhibitors. We hypothesize that EGFR inhibitor resistance in SCCHN is due in part to activation of AKT secondary to genomic alterations in the PI3K/AKT pathway. This application will identify genomic alterations in the PI3K/AKT pathway associated with resistance to EGFR inhibitors and characterize the functional significance of these alterations. This proposal takes advantage of the largest known repositories of SCCHN tumor samples collected immediately prior to initiating clinical trial therapy with an EGFR inhibitor. TaqMan(R) SNP Genotyping Assay and microwestern arrays, a novel technology developed at University of Chicago, will be used to determine if EGFR inhibitor resistant tumors harbor a higher frequency of PI3K/AKT pathway alterations and activation. Furthermore, the most common alterations found in human tissues will be recapitulated using preclinical models to determine the phenotypic and mechanistic changes associated with each. In addition, this application will determine whether the combination of PI3K/AKT and EGFR inhibitors are more effective than either agent alone in SCCHN preclinical models and identify the mechanistic underpinnings of efficacy. The activity of two distinct PI3K/AKT inhibitors will be characterized with and without EGFR inhibitors in vitro and in vivo. An interaction index will determine whether combination therapy is synergistic or additive. Furthermore, the mechanisms underlying combinatorial efficacy will be examined. This proposal is expected to define a molecular phenotype associated with resistance to EGFR inhibitors in SCCHN; understand the functional significance and therapeutic implications of PI3K/AKT pathway genomic alterations in SCCHN; and provide critical rationale to begin clinical trials and select appropriate patients for therapy with single-agent EGFR inhibitors with or without PI3K/AKT inhibitors in SCCHN. The impact of this proposal will be to fundamentally alter the way SCCHN patients are treated by determining those that are unlikely to benefit from EGFR targeted therapy. This proposal applies hypothesis-driven, innovative molecular methods to an unparalleled tumor sample set and explores novel targeted agents in a disease where research on the pathogenicity of PI3K/AKT pathway alterations has been sparse.